Vette-4-Life

Looking for someone to point me in the direction of what might be the cause for the following.

My tach has started showing the wrong RPM's over the last few days. Example: sometimes shows car turning 2000 rpm while at idle, idle is typically 800 rpm. Today tach was fine.

Could suspect problem be filter, or circuit board?


:steering:

bigvette1

What year? Mechanical drive off dist. or tach circuit card?

Vette-4-Life

1980

theoUK

Could be the filter on its way out - it's located in the line from the "tach" output on the distributor, if you follow that line, you'll come to it (provided someone hasn't pulled it out already) Apparently they corrode internally over time. You cant get a direct replacement these days, but i found a guy who is making a funtional replacement - check out
http://my.execpc.com/~rodney1/corvette/
I've got the same problem with mine, but i haven't got round to ordering a new one yet..
Let us know if this works for you...
By the way, there seems to be a bit of disagreement as to whether the filter is necessary... It seems the tach will work without one, but how long for is the big question. My opinion at the moment would be to keep on the safe side and use the filter, 'cos i don't really understand enough about the system yet to know if you can get away without one!
If a new filter doesn't do it, the board is probably fried.....

bigvette1

The filter is to filter out transient spikes from the mag pickup in the dist. Too many spikes and the circuit card get fried.